Percussive rock drill bit with asymmetric wing

ABSTRACT

A percussive rock drill bit includes a steel bit body and carbide button inserts mounted in a front cutting face thereof. The bit body includes a passage intersecting the front cutting face for conducting a flushing/cooling medium to the front cutting face. The flushing/cooling medium travels to an outer periphery of the bit body and travels upwardly within flushing grooves formed in the outer periphery of the bit body. Portions of the bit body situated between successive ones of the flushing grooves constitute wings of the bit body. Some of the button inserts constitute gauge inserts. Only a gauge insert is mounted in each wing. At least some, possibly all, of the gauge inserts are offset circumferentially from a center of the respective wing toward a trailing end of the wing.

BACKGROUND OF THE INVENTION

The present invention relates to percussive rock drill bits, such asused in percussive down-the-hole hammers and top-hammer drills, forexample, which bits comprise a steel body carrying hard button inserts.The body includes a plurality of wings. In particular, the inventionrelates to such drill bits wherein only a single gauge button isdisposed in each wing of the drill bit.

Such a drill bit 10 is depicted in FIG. 1 (and also in U.S. Pat. No.5,025,875). The drill bit includes a steel bit body 12 forming a frontcutting face that is intersected by two fluid passages 14 for conductinga flushing/cooling medium (e.g., air) to the front cutting face. Eachpassage 14 communicates with a radial channel 16 in the cutting face forconducting the flushing/cooling medium to an outer periphery of the bitbody, in particular, to respective longitudinal flushing grooves 18′formed in the bit body for facilitating the longitudinal flow of themedium. Additional longitudinal flushing grooves 18 are provided, all ofthe flushing channels 18, 18′ being in circumferentially spacedrelationship with one another. Disposed between successive flushingchannels in the circumferential direction are so-called wings 20, 20′ ofthe bit body, wherein the wings 20′ are situated immediately behind theflushing grooves 18′ with reference to the rotation direction d.

Mounted in longitudinal holes formed in the front cutting face arebutton inserts 22, 23, 23′ formed of a hard material such as cementedcarbide, especially tungsten carbide. The inserts 23, 23′ are mounted inthe wings 20, and are known as gauge inserts because they define thediameter of the hole being cut. Two of the gauge inserts 23′ are mountedin the wings 20′ that are situated immediately behind the flushinggrooves 18′. The remaining gauge inserts 23 are mounted in the otherwings 20.

FIG. 1 depicts a type of drill bit wherein only a single gauge insert23, 23′ is disposed in each wing 20, 20′ (other conventional types ofdrill bits may have more than one gauge insert in each wing, but thepresent invention does not pertain thereto.) Typically, in such a drillbit, each gauge insert is located at the center of the respective wing,with reference to a circumferential dimension of the wing. In otherwords, if the direction of rotation of the drill bit is in the directiond, then the distance A from the center of the gauge insert 23, 23′ to aleading edge 24 of the wing 20, 20′ is equal to the distance B from theinsert center to the trailing edge 26 of the wing, this being the casefor all of the gauge inserts.

During rotation of the drill bit, the leading portion of each wing,i.e., the leading edge 24 of the wing, is more exposed than is thetrailing edge 26. Consequently, the leading edge wears more rapidly,sometimes limiting the life of the bit. This can happen while thetrailing edge remains relatively intact. That is especially true of thewings that are situated immediately downstream of the flushing grooves18′ disposed at radially outer ends of the radial channels 16.

It has been proposed in the prior art to deal with the above-describedwear problem by making the flushing grooves narrower, thus extending thetotal wing length and the total amount of steel. Another solution is toincrease the hardness and wear resistance of the steel. Yet anothersolution is to add wear protection buttons on the outside of the wing.It is not uncommon to put the wear protection buttons on the leadingledge. However, these solutions have drawbacks in regards to flushingcapacity of the design, fatigue resistance of the steel and/ormanufacturing cost.

SUMMARY OF THE INVENTION

A percussive rock drill bit includes a bit body and a plurality ofbutton inserts mounted in the bit body. The bit body forms a frontcutting face and a peripheral surface. At least one passage intersectsthe front cutting face for conducting a flushing/cooling medium to thefront cutting face. The peripheral surface has a circumferentiallyspaced flushing grooves formed therein. Portions of the bit body whichare disposed between successive flushing grooves comprise wings. Eachwing having a leading edge and a trailing edge. The button inserts areformed of a material harder than the material of the bit body. Some ofthe button inserts constitute gauge inserts and are mounted in thewings. There is only one gauge insert mounted in each wing. At least oneof the gauge inserts is offset circumferentially from a center of therespective wing by a distance equal to at least five percent of acircumferential length of the wing.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements and in which:

FIG. 1 is a front elevational view of a prior art cutting bit of thetype having only one gauge insert in each wing;

FIG. 2 is a view similar to FIG. 1 depicting a first embodiment of thepresent invention;

FIG. 3 is a view similar to FIG. 2 depicting a second embodiment of theinvention; and

FIG. 4 is a perspective view of a third embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

A first embodiment of a percussive rock drill bit 10A according to theinvention is depicted in FIG. 2. The parts thereof corresponding to theprior art drill bit of FIG. 1 are provided with the same referencenumerals. The structure of the drill bit 10A is identical to the priorart drill bit 10 of FIG. 1, except for the two gauge inserts 23A′ whichare mounted in the wings 20′ situated immediately behind the twoflushing grooves 18′ that are located at the radially outer ends of theradial channels 16. Those gauge inserts 23A′ (two in number in FIG. 2)are not located at the circumferential center of the wings 20′ as in theprior art, but rather are located closer to the trailing edge 26. (Thatis, in FIG. 2, A′>B′.) That is not true of the other gauge inserts 23,wherein A=B.

As a result, the amount of steel disposed between each insert 23A′ andthe leading edge 24 of the respective wing 20′ is increased as comparedto the prior art, whereby there is more steel to withstand the higherrate of wear during a drilling operation. Accordingly, the life of thedrill bit is increased as compared with the prior art.

The amount by which the gauge insert 23A′ is offset from the wing centeris at least 5% of the circumferential length L of the wing 20′. That is,(A′−L/2)>0.05L in FIG. 2.

The bit can be used in percussive down-the-hole hammers as well as intop-hammer drills. It should be noted, however, that since down-the-holehammers are rotated in a clockwise direction, whereas top hammer drillsare rotated in a counterclockwise direction, the direction in which thewing inserts are offset from wing midpoint is different, depending uponthe type of drill being used.

The embodiment of the invention depicted in FIG. 3 is identical to theembodiment of FIG. 2, except that in FIG. 3 every one of the gaugeinserts 23, 23A′ is offset rearwardly from the center of the respectivewing. That is, preferably at each wing (A−L/2)>0.05L, or (A′−L/2)>0.05L.

In the embodiment according to FIG. 4, a different type of percussiverock drill bit 30 is depicted wherein the front cutting face isintersected by flushing passages 31, but no radial channels are present.Also, the gauge inserts 33 are situated in recesses 35 formed in eachwing 38. Each of the gauge inserts 33 is offset rearwardly from a gaugecenter. That is in FIG. 4, (A−L/2)>0.05L.

What is claimed is:
 1. A percussive rock drill bit comprising: a bitbody forming a front cutting face and a peripheral surface, at least onepassage intersecting the front cutting face for conducting aflushing/cooling medium to the front cutting face, the peripheralsurface having circumferentially spaced flushing grooves formed therein,portions of the bit body disposed between successive flushing groovescomprising wings, each wing having a leading edge and a trailing edge; aplurality of button inserts mounted in the bit body, the button insertsformed of a material harder than the material of the bit body, some ofthe button inserts constituting gauge inserts and mounted in the wings,there being only one gauge insert mounted in each wing, wherein thecutting face includes a radial channel associated with the at least onepassage for conducting flushing/cooling medium from the passage to oneof the flushing grooves, one of the wings being situated immediatelybehind the one flushing groove, the gauge insert mounted in the one wingconstituting an offset gauge insert which is offset circumferentiallyfrom a center of the one wing in a direction away from the leading edge,by a distance equal to at least five percent of a circumferential lengthof the wing.
 2. The drill bit according to claim 1 wherein there are atleast two passages, and at least two radial channels, wherein at leasttwo of the gauge inserts are offset from centers of their respectivewings.
 3. The drill bit according to claim 1 wherein each of the gaugeinserts on the bit body constitutes an offset gauge insert which isoffset from the center of its respective wing in a direction away fromthe leading edge thereof by at least five percent of the wing length. 4.The drill bit according to claim 1 wherein each wing includes a recess,the gauge inserts being mounted in respective ones of the recesses. 5.The drill bit according to claim 1 wherein the bit body is formed ofsteel, and at least some of the button inserts are formed of cementedcarbide.
 6. The drill bit according to claim 1 wherein the bit body isformed of steel, and at least some of the button inserts arediamond-enhanced.
 7. A percussive rock drill bit comprising: a bit bodyforming a front cutting face and a peripheral surface, at least onepassage intersecting the front cutting face for conducting aflushing/cooling medium to the front cutting face, the peripheralsurface having circumferentially spaced flushing grooves formed therein,portions of the bit body disposed between successive flushing groovescomprising wings, each wing having a leading edge and a trailing edge; aplurality of button inserts mounted in the bit body, the button insertsformed of a material harder than the material of the bit body, some ofthe button inserts constituting gauge inserts and mounted in the wings,there being only one gauge insert mounted in each wing, all of the gaugeinserts being offset circumferentially from a center of the respectivewings in a direction away from the leading edge thereof, by a distanceequal to at least five percent of a circumferential length of therespective wing.